I hate plumbing

The toilet has been sort of rocking back and forth in the one bathroom, like the seal is broken, and so today we took it off and replaced the seal. We have discovered that the base of the toilet doesn't actually rest on the floor. It sits about half a centimeter up, and is supported entirely by the pipe. (!) Now that we've pulled off the strange rigid caulking that was on the outside of the toilet base, it rocks back and forth, even though we've tightened it plenty and it has a new seal. I'm going to put spray foam in there to keep out...well, anything undesirable coming up from outside through the floor, but I think I probably need some kind of wood pieces or something to help support it as well? This bathroom has been a nightmare from the beginning. The shower leaks in multiple places and the water problems have been there for years, so long that the door to the shower and the door to the bathroom are not longer at right angles. Scary, huh? I just hope we move before the whole thing goes. I clean it often, but I feel crawly thinking what the underside of the bumpy linoleum must look like...